When Admixtures Turn Us into Chemists
Admixture: ingredients (other than water, aggregate, hydraulic cement, and fiber reinforcement) added to a batch of concrete or mortar before or during its mixing.
Chemical admixtures are now a routine part of concrete work. They react with the components inside the slab, and the goal is the same as it has always been: high-quality concrete that sets and gains strength on schedule.
However, chemical reactions are a chemist’s world. Admixtures play an increasingly prominent role in concrete installation, and that makes chemists out of building contractors.
- “How Beneficial Is an Admixture?”
- The Influence of Relative Humidity (RH)
- Moisture Measurement
- Additional Reading
“How Beneficial Is an Admixture?”
The answer is changing as quickly as the new admixture ingredients. However, we can generally observe the main effects of those most widely applied to concrete.
Superplasticizers, also called high-range water reducers, are widely used. According to the American Concrete Institute (ACI), they can cut a mix’s water content by 30% or more without excessive set retardation. Less mix water can mean less water that has to dry out of the slab.
Water-reducing admixtures are made from different materials, and they don’t all behave the same way. Some, such as lignosulfonate-based water reducers, can slow setting or entrain air, depending on the formulation and dose. Unintended air reduces strength. That is not the same as air entrainment, the deliberate addition of microscopic air cells to protect concrete against freeze-thaw damage.
Modern superplasticizers based on polycarboxylate polymers are more effective than older types, retard setting less, and develop strength faster, according to ACI.
Many other factors influence concrete installation: cement composition, its alkali content, and particle distribution to name a few. For flooring, though, the question is whether an admixture helps the slab dry. While admixtures can speed the curing process, they do not always benefit the drying process of a concrete slab. Concrete dries only as moisture moves up through the slab and evaporates from the surface. That is the goal.
The Influence of Relative Humidity (RH)
The RH of the surrounding air affects how quickly concrete dries. Admixtures may provide a chemical means of speeding up drying, but they can come with trade-offs for the concrete itself. If the slab hasn’t dried to the RH limit the floor covering manufacturer specifies, the flooring installed over it is at risk.
Chemical admixtures may also be incompatible with flooring applications. Moisture and the high pH of concrete can break down flooring adhesives, and incompatible admixtures can further complicate matters. It is wise to investigate all thoroughly before attempting such feats of flooring chemistry.
Moisture Measurement
You can track how a slab is drying by measuring the RH inside it. Wagner Meters’ Rapid RH® system is designed for in-situ RH testing in compliance with ASTM International Standard F2170.
It may not resolve the technical evolution of admixtures, but moisture management remains at the core of every successful concrete slab installation.
Free Download: 4 Reasons Why Your Concrete Is Taking Forever to Dry
Additional Reading
ACI Education Bulletin E4-12, Chemical Admixtures for Concrete. Farmington Hills, MI: American Concrete Institute.
Ramachandran, V.S. (Ed.) Concrete Admixtures Handbook: Properties, Science, and Technology, 2nd Ed. Park Ridge, NJ: Noyes Publications, 1995.
Jason has 20+ years’ experience in sales and sales management in a spectrum of industries and has successfully launched a variety of products to the market, including the original Rapid RH® concrete moisture tests. He currently works with Wagner Meters as our Rapid RH® product sales manager.
Last updated on October 22nd, 2026
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